1. Field of the Invention
The present invention relates to a recording-density control method for an image recording apparatus for recording images that controls recording density by having nozzle array components that are each made of a plurality of nozzles for discharging a uniform ink color.
2. Description of the Related Art
Image recording apparatuses such as printers and copying machines employ inkjet print recording, thermal recording, and thermal transfer recording.
Inkjet print recording uses a nozzle array component (recording head) having a plurality of nozzles arranged in an approximately linear manner for recording the recording dots.
One of the methods used by such image recording apparatuses is the full-line type method shown in FIG. 1.
The image recording apparatus in FIG. 1 has a nozzle array component (recording head) for creating a uniform color that is formed by nozzle array components (recording heads) 16a-16f being fixed and arranged by a carriage 15 so that each of the recording ranges are adjacent to each other or in a position in which a part of the range overlaps in the direction in which the recording medium 11 is being carried. The recording medium 11 to be recorded is carried in the direction indicated by the arrow 14 in FIG. 1 by a roller 13 that is driven by a motor 12, is at a position in which the medium 11 faces the ink discharging side of nozzle array components 16a-16f, and image data is separately recorded by nozzle array components 16a-16f.
Next, the nozzle array component (recording head) used in an image recording apparatus with such a configuration is explained.
FIG. 2A is a diagram that schematically shows a nozzle array component(recording head) from the ink discharge side.
In FIG. 2A, a plurality of nozzles 22 for discharging ink are arranged in an approximately linear manner over the width 23 on the ink discharging side 21.
In such a nozzle array component (recording head), the recording density characteristic may be different for each nozzle array component (recording head), or the recording density characteristic may depend on the position in which the plurality of nozzles 22 are arranged, as shown in FIG. 2B.
FIG. 2B shows a scanner output value (recording density) in a case in which image data with a uniform color and the same tone is recorded on a recording medium by a uniform driving signal (driving parameter) with all of the plurality of nozzles 22, and the recorded recording medium is read by a scanner. According to the recording density characteristic in FIG. 2B, there is a difference in the output values between the edge and center of the recording head; consequently, an uneven density exists in the recording result.
As technology for solving such a problem, Patent Document 1 (Japanese Patent Application Publication No. 10-44519) discloses a serial type inkjet image recording apparatus and image recording system for improving density unevenness caused by the difference in density characteristics of the recording head.
The image recording apparatus and image recording system comprise two recording heads, recording head A and a recording head B, arranged in a carriage with a prescribed amount of space between them. When recording on the recording medium by dividing the scanning areas by the two recording heads, corrections are made to signal values input into both of the recording heads so that the recording density produced by the recording head A and the recording density produced by the recording head B can be the same.
FIG. 3 shows a conventional method of controlling density differences for nozzle array components (recording head, in the case of the first through third recording heads in FIG. 3) in an image recording apparatuses such as the one shown in FIG. 1.
FIG. 3A shows output values (scanner output values) when recording image data on matter with a uniform color and tone by all nozzles of the first through third recording heads. In other words, FIG. 3A shows the density characteristics of the first through third recording heads. In FIG. 3A, the scanner output value is on the vertical axis, and the value becomes larger as the surface of the recorded matter becomes brighter (as reflectance on the recorded matter becomes higher).
In general, the scanner output values are low when the density value is high. In the following explanation, the scanner output values are employed as values indicating the density.
In order to match the density at the connections of the first through third recording heads, the density characteristic of each of the recording heads should be examined at the beginning of the process. The examination method should be such that a test recording of image data with a uniform color and tone is conducted by an image recording apparatus and the recording density of the recorded medium of the test recording is measured.
Accordingly, in the image recording apparatus with the first through third recording heads, in order to match the density of the second recording head adjacent to the first recording head designated to be a reference, a first test recording is conducted on the recorded medium.
Next, the recording density of the recorded medium of the test recording is measured by a scanner, and from the difference between the density of the right end of the first recording head and the density of the left end of the second recording head, the correction amount of a driving parameter of the second recording head (such as the application voltage/application time of each nozzle of the recording head) is calculated, and the correction is performed on the basis of the calculated value. As a result, the densities on the right end of the first recording head and the left end of the second recording head should match. FIG. 3B shows such a state.
Next, the image recording apparatus performs test recording again since the density characteristic of the second recording head changed with the above correction. The recording density of the recorded medium of the test recording is measured by a scanner, the correction amount of a driving parameter of the third head is calculated from the recording densities on the right end of the second recording head and the left end of the third recording head, and the correction is performed on the basis of the calculated value. As a result, on the right end of the second recording head and the left end of the third recording head, the densities should also match. FIG. 3C shows such a state.
Because there is in general a nonlinear relationship between the driving parameter and the recording density, after the correction of the second recording head adjacent to the first recording head designated to be a reference, the density of the other recording head cannot be controlled using the result in the conventional methods not employing the information.
In the image recording apparatus with the first through third recording heads, as shown in FIG. 3A through FIG. 3C, the correction amount can be calculated using only the above-explained procedures and correction processing can be performed because the connections of the three adjacent recording heads are matched.
However, in an image recording apparatus comprising a recording head discharging an ink of a uniform color with a larger number of recording heads, calculation of the correction amount corresponding to the number of recording heads has to be repeated.